In manufacturing semiconductors, finer and finer patterning of resist images has been required and attempted to attain higher integration. In order to satisfy this requirement, there have been made development and improvement of lithographic techniques using short-wavelength exposure tools such as deep-UV. As photoresists showing high performance when exposed to deep-UV, there have been known chemically amplified, deep UV (100-300 nm) positive- or negative-working photoresists. While such exposure tools in combination of the chemically amrplified, high performing photoresists enable one to pattern with less than quarter micron line width, there still remain several other problems that need to be solved in achieving such high resolutions. One such problem well known in the art is called "standing waves" arising from interference between incident light and reflected light of the incident light reflected on the substrate surface. Another problem is the difficulty in uniformly controlling the line width in single layer resist process due to thin film interference effects resulting from highly planar and non-planar substrates. Various reports have been made. For example, there are illustrated the report of M. Horn in Solid State Technology, Nov. 1991, p. 57, the report of T. Brunner, Proc. SPIE, vol. 1466 (1991), p.297, etc. In addition, as a cause which causes pattern distortions, there is the phenomenon called reflective notching which is caused by light reflected angularly from topographical features. This is discussed by M. Bolsen, G. Buhr, H. Merrem, and K. Van Werden, in Solid State Technology, Feb. 1986, p.83.
Lithographic techniques to solve the problems upon forming patterns on reflective topography include addition of dyes to the photoresists as described in U.S. Pat. Nos. 4,575,480 and 4,882,260, etc. However, when a dye is added to the photoresist to form a film having high absorption to the light of exposing wavelength, drawbacks such as decrease in resist sensitivity, difficulties during hardening processes, thinning of the resists in alkaline developers and sublimation of the dyes during baking of the films are encountered. In addition to the technique of adding dyes to photoresists, top surface imaging (TSI) processes, multilayer resists (MLR) method as described in U.S. Pat. No. 4,370,405 also help solve the problems associated with reflection but such methods are not only complex but also expensive and not a preferred method. Single layer resist (SLR) processes dominate semiconductor manufacturing because of their cost-effectiveness and simplicity.
Another strategy to eliminate the interference of lights is to reduce the substrate reflectivity through the use of so-called bottom anti-reflective coatings (BARCs). These coatings have the property of absorbing the light which passes through the photoresist and not reflecting it back and prevent the reflection by the substrate. As the bottom anti-reflective coatings, there are known inorganic types and organic types. Inorganic types include coatings of TiN, TiNO, TiW or inorganic polymer of 300 .ANG. in thickness, as described in C. Nolscher et al., Proc. SPIE, vol. 1086 (1989), p.242, K. Bather, H. Schreiber, Thin Solid Films, 200, 93 (1991), G. Czech et al., Microelectronic Engineering, 21 (1993), p.51. In addition to these coatings, there are also known inorganic coatings such as a titanium coating, a chromium oxide coating, a carbon coating, an .alpha.-silicon coating, etc. These inorganic anti-reflective coatings are usually formed by vacuum deposition, CVD, sputtering or the like. However, formation of such coatings requires accurate control of the film thickness, uniformity of film, special deposition equipment, complex adhesion promotion techniques prior to resist coating, separate dry etching pattern transfer step, and dry etching for removal. Some of the inorganic coatings can not be used in manufacturing integrated circuits due to their conductivity.
On the other hand, as the organic anti-reflective coatings, there are illustrated those formulated by adding dyes which absorb light of the exposure wavelength to a polymer coating (Proc. SPIE, Vol. 539 (1985), p.342). This dye-containing, anti-reflective coating can be formed on a substrate in the same manner as with photoresists, and does not require any special equipment as is different from the inorganic anti-reflective coatings. However, they involve such problems as 1) separation of the polymer and dye components during spin coating, 2) dye stripping into resist solvents, and 3) thermal diffusion into the resist upon the baking process. All these factors cause degradation of resist properties, and therefore the technique of adding a dye to the polymer coating to form an anti-reflective coating is not a preferred one.
Chemically binding the dyes to film forming polymers is another option. Fahey, et al. (Proc. SPIE, Vol. 2195, p.422) report to use a reaction product obtained by reacting an amino group possessing dye with the anhydride groups of poly(vinylmethyl ether-co-maleic anhydride) as the material for forming the anti-reflective coating. The problem with this type anti-reflective coating material is that the reaction between amine and the anhydride groups are not always 100% complete and this leads to presence of free amines (refer European unexamined patent application No. 0583205, page 5, lines 17-20). The remaining free amine causes poisoning at the interface between the anti-reflective coating and the resist coating especially when a chemically amplified resist is used as the resist, and this leads to a problem called footing: incomplete dissolution of the exposed resist upon development. In addition, there arises another problem that free dye molecules sublime during the baking process and deposits on the fabrication instruments and causes contamination problem as well as health hazard to the workers. One more problem of such compositions is that imide compounds are poor in their solubility and need polar solvents normally not used in photoresist formulations. It would be ideal to use the same solvent for both the photoresist and the anti-reflective coating since the same coating apparatus is often used for applying the photoresist and the anti-reflective coating. Further, the by-product of imidization reaction, water, causes coating defects during film formation.
Another system Fahey et al. propose is materials wherein a copolymer of methyl methacrylate and 9-methylanthracene methacrylate is used as the anti-reflective coating. Again this system also shows footing problem due to the diffusion of photo-generated acid into the anti-reflective coating when a chemically amplified resist is used as the resist (Proc. SPIE, Vol. 2195, p. 426) as well as intermixing of the resist material and the anti-reflective coating material. Such polymers are also insoluble in preferred solvent in the art such as propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, etc.
U.S. Pat. No. 5,234,990 discloses polysulfone and polyurea resins which possess inherent light absorbing properties at particular deep ultra violet wavelengths. These condensation products have poor film forming property on a patterned wafer and therefore bad step-coverage and also formation of cracks perhaps due to high Tg and rigid structures of such polymers. Ideally, a bottom anti-reflective coating materials should be soft for good step coverage property before baking and also hardened at least after as baking to prevent intermixing of the photoresist and the anti-reflective coating as well as diffusion of the photo-generated acid.
Further, European unexamined patent application No. 542 008 discloses an anti-reflective coating composition capable of forming a hardened anti-reflective coating after being applied, which comprises a phenolic resin binder, melamine type cross-linking agents and a thermal or photo acid generators. Such compositions are poor in their storage stability due to the presence of the cross-linking agents and acid generators leading to high incidence of film defects, and their etch rate is very slow due to the presence of rather large amounts of aromatic functional groups.
In summary, a good bottom anti-reflective coating material should satisfy the following properties:
a) good film forming property; PA1 b) high absorption at the desired exposure wavelength; PA1 c) no intermixing with the photoresist; PA1 d) etch rate much higher than the photoresist; PA1 e) good step coverage on topography; PA1 f) at least six months shelf-life stability; and PA1 g) the composition should be dissolved in an edge-bead rinse (EBR) solvent. PA1 R is a hydrogen atom or an alkyl group; R.sub.1 represents an alkylene group, a substituted alkylene group, a cycloalkylene group, a substituted cycloalkylene group, a phenylene group or a substituted phenylene group; R.sub.2 represents an optionally substituted, vinyl group-containing phenyl group, --OR.sub.4 or --COOR.sub.4, in which R.sub.4 is an alkyl group having a double bond or epoxy group; R.sub.3 is a halogen atom, a cyano group, an acetate group, --COOH, --CONH.sub.2, a substituted or non-substituted phenyl group, --COOR.sub.5 or --OR.sub.5, in which R.sub.5 represents a substituted or non-substituted straight-chained, cyclic or branched alkyl group, or an alkyl or aryl group containing an ester or carbonyl group; X is either O or S; Y is either O or N.sub.6 group in which R.sub.6 is a hydrogen atom, an substituted or non-substituted phenyl or cyclic, straight-chained or branched alkyl group; D is an organic chromophore which absorbs the exposed wavelength (100-450 nm) and represents a substituted or non-substituted benzene ring, condensed ring, or heterocyclic ring bound directly or through an alkylene group; and m and n represents any number above zero, while o is any number including zero. PA1 R is a hydrogen atom or an alkyl group; R.sub.2 represents an optionally substituted, vinyl group-containing phenyl group, --OR.sub.4 or --COOR.sub.4, in which R.sub.4 is an alkyl group having a double bond or epoxy group; R.sub.3 is a halogen atom, a cyano group, an acetate group, --COOH, --CONH.sub.2, a substituted or non-substituted phenyl group, --COOR.sub.5 or --OR.sub.5, in which R.sub.5 is a substituted or non-substituted straight-chained, cyclic or branched alkyl group, or an alkyl or aryl group containing an ester or carbonyl group; Y is either O or NR.sub.6 group in which R.sub.6 is a hydrogen atom, a substituted or non-substituted phenyl or cyclic, straight-chained or branched alkyl group; D is an organic chromophore which absorbs the exposed wavelength (100-450 nm) and represents a substituted or non-substituted, benzene ring, condensed ring, or heterocyclic ring bound directly or through an alkylene group; and m and n represents any numbers above zero, while o is any number including zero. PA1 R is a hydrogen atom or an alkyl group; R.sub.1 represents an alkylene group, a substituted alkylene group, a cycloalkylene group, a substituted cycloalkylene group, a phenylene group or a substituted phenylene group; R.sub.2 is an optionally substituted, vinyl group-containing phenyl group, --OR.sub.4 or --COOR.sub.4 in which R.sub.4 is an alkyl group which has a double bond or epoxy group; R.sub.3 is a halogen atom, a cyano group, an acetate group, --COOH, --CONH.sub.2, a substituted or non-substituted phenyl group, --COOR.sub.5 or --OR.sub.5 in which R.sub.5 is a substituted or non-substituted straight-chained, cyclic or branched alkyl group, or an alkyl or aryl group containing an ester or carbonyl group; X is either O or S; Y is either O or NR.sub.6 group in which R.sub.6 is a hydrogen atom, an optionally substituted phenyl or cyclic, straight-chained or branched alkyl group, D is an organic chromophore which absorbs the exposed wavelength (100-450 nm) and represents a substituted or non-substituted, benzene ring, condensed ring, or heterocyclic ring bound directly or through an alkylene group; and m and n represents any number above zero, while o is any number including zero.
Unfortunately none of the available bottom anti-reflective coating satisfies these properties.
The present invention provides an anti-reflective or light-absorbing coating material which fulfils the above-described various properties; a composition containing this material and useful for forming an anti-reflective coating such as a bottom anti-reflective coating or a light-absorbing coating; a process for manufacturing the composition, and an anti-reflective or light absorbing coating using the material or the composition; a method for forming the coatings; a method for forming a resist pattern; and a process for manufacturing integrated circuits.
The first object of the present invention is to provide a composition capable of forming an anti-reflective coating or a light absorbing coating which reduces problems associated with reflected light from the substrate and topography during pattern formation.
The second object of the present invention is to provide a composition capable of forming an anti-reflective coating or a light absorbing coating having improved adhesion to micro-electronic substrates, very good coating uniformity and no particle formation.
The third object of the present invention is to provide a composition capable of forming an anti-reflective coating or a light absorbing coating that has significantly higher etch rate than the photoresist material applied on top of it.
The fourth object of the present invention is to provide novel polymers applicable for anti-reflective coatings or light absorbing coatings containing cross-linking and highly light-absorbing functions in a single molecule, and soluble in similar or same solvent as the photoresist material applied on top of it.
The fifth object of the present invention is to provide novel polymers applicable for anti-reflective coatings or light-absorbing coatings containing intrinsically cross-linking and highly absorbing functions in a single molecule eliminating the need for additives with cross-linking and highly light-absorbing functions.
The sixth object of the present invention is to provide novel polymers which are capable of curing (cross-linking) at the baking temperatures of the resulting anti-reflective coating or light absorbing coating to acquire such a high hardness after being baked that it is impossible for the photoresist top layer to cause intermixing with the coating, which cause no diffusion of an acid generated in the subsequent steps and thereby prevent footing.
The seventh object of the present invention is to provide novel polymers which have chromophores capable of highly absorbing light of exposure wavelength and can sufficiently absorb light in a film thickness of 30 to 300 nm, and which can form an extremely thin anti-reflective coating or a light absorbing coating.
The eighth object of the present invention is to provide a bottom anti-reflective coating or a light absorbing coating having good light absorbing properties.
The ninth object of the present invention is to provide a method for easily forming a resist pattern with high resolution.
The tenth object of the present invention is to provide a method for easily manufacturing an integrated circuit with higher integration.
Other objects of the present invention will become apparent from the following descriptions.